Two months ago, I gave in to temptation and bought the Jawbone UP3 wristband. (Previously, I wore the Jawbone UP24, which was an extraordinarily comfortable and durable device with excellent customer service. My primary motivation for upgrading was to get the pulse feature. I'm an avid runner and updates on my heart rate just seemed like something that would be cool to know.
Here are some brief thoughts on the device when compared with its predecessor. The app for the Jawbone UP3 is much, much better than that of the UP24, which almost never worked by the time I upgraded. (It basically required a daily phone reset in order to sync my device. This had the effect of training me not to bother checking the app but for once or twice a week, tops. More on this in a minute.) It now seems clear that Jawbone simply abandoned the old app in favor of the new, or at least, has its B-team working on that one. (The old devices and new apps are incompatible.) Regardless, the new app is fast and fun to use. It's functionally identical, but it actually works. It's almost worth the upgrade for that alone.

In terms of comfort, once you have the device strapped to your wrist, it's easy to forget about. It has a very low profile, and on the rare occasion that it catches on something, it's not a panic-inducing concern. I can't imagine how one might damage the rubber-like band, and the two-inch plastic "device" component of the band seems well-hardened and scratch resistant. Either way, it's not like you're going to damage the nonexistent screen, or a Jony Ive designed, multi-axis milled, cold-forged-alloy-and-diamond-carbon-coated case. If anything, the rubber-and-plastic band is more durable than the Apple Watch in daily use, as there's no high polish in need of constant cradling. It would be hard to spot a scratch on this thing.

(N.b. that this isn't really to compare the two devices, which serve entirely different purposes. The Apple Watch is a very attractive watch that happens to track activity. The Apple Watch wants to be seen. The Jawbone UP series tracks activity, and wants to stay hidden.)

The UP3 seems close in appearance and fit to those Livestrong bands. (I've never actually worn one, so I cannot comment on the similarity of comfort.) In practice, it takes a couple of weeks to really figure out your fit and learn how to strap on the device. It's not a watch clasp, exactly, but a weird overlap clipping mechanism that requires you to stretch the band with your non-dominant hand, align the clasps and clip them. The device was intended originally to be waterproof, and with that in mind the clasp makes perfect sense. Regardless of the headache that is its design, if you only have to remove it once a week, there are no worries. Unfortunately, the device is not waterproof, which means daily removal while you shower. (It is water resistant, however. I even cleaned my pool yesterday while wearing it. So technically you could wear it in the shower, I guess, but it seems like it would be a pain to rinse the soap away from underside.)

The battery life is much worse than the Jawbone UP24. Within six days, the device is dead, and I never realize it until it's too late. The previous model trained me to just forget about it. It was always there, always working, this immortal machine powered as if by plutonium. This one is like a really healthy octogenarian. There's no reason to worry, exactly, but you know the end could come at any moment. The charger, meanwhile, is a mess. Just this weird, terrible dongle-like thing whose magnetic contacts are impossible to properly align the first five or six times you go to charge the device. This is only like a minute of my week lost, but I'm glad my pulse isn't measured for that minute; my frustration with and bafflement of the design would throw off my average.

The pulse measurement is passive. That is to say, you can't push a button and get a reading. It happens when it happens and that'll just have to do. It measures both resting and passive heart rate. It doesn't give a whole lot of guidance for the information it collects, and I suspect that has something to do with federal regulations. Its advice is usually something to the effect of: "Your heart rate is slightly higher than last week. Try getting more sleep." I'm pleased to have the readings, though, and it really is a motivator to remain on top of my running. My RHR is generally in the high-40s and I'd like to keep it there, or even get it a bit lower. (Now that fitness is measured by how rarely one's heart has to beat to keep you alive.)

Lastly, the cost. I'm not sure of the price at which it premiered, but earlier this year it ran $179, which was a shade too much. $159 would have made it a real bargain. But the price has since dropped to $129, making it an absolute steal. Despite its minor frustrations, I heartily recommend the device. It does what it sets out to do, and does it well.